Ultrasound in trauma, whether in the case of an individual patient or that of a multiple-casualty incident, has an important role in evaluation and immediate triage. The ultrasound examination in the trauma room is brief and focused and should answer a single relevant question: “Is there a hemoperitoneum?” In this article, the usefulness of focused assessment with sonography for trauma (FAST) is reviewed for the different types of cases arriving in the trauma room: blunt versus penetrating injuries, stable versus unstable patients, and children versus adults. Sonographic technique and controversies pertaining to protocol and to practice domain are also discussed.